具反相功率分配器功能之微帶天線及其於陣列天線之應用

Abstract

本論文提出一應用於陣列天線之具反相功率分配器功能微帶天線，此微帶天線由兩層基板及三層金屬構成，信號由下層微帶線饋入，穿越地平面的槽孔，經不同尺寸的雙金屬連通柱進入上層微帶天線，微帶天線兩側由高阻抗線接出，用以饋入上層兩側的子陣列合成一陣列天線。藉由改變下層微帶線末端之開路線、雙金屬連通柱的尺寸、間距及其與微帶天線的相對位置，可以準確控制上層兩側輸出的功率比例及相位差，論文中亦歸納出此元件的設計準則，並以此微帶天線合成出應用於77 GHz車用防撞警示雷達之陣列天線。 實用上為將系統體積最小化，天線與射頻電路走線須分置於電路板的上下兩層，將上層的使用面積完整保留給天線，信號從下層電路至上層天線須一轉層饋入結構，此外，若此饋入結構不須擺在陣列天線的中心，則下層電路走線的自由度將可提升，本文提出之具反相功率分配器功能微帶天線，即具備此二特性，包含轉層饋入功能及偏側饋入陣列天線的能力。

In this thesis, a microstrip antenna with 180 degree out-of-phase power divider function and its application to array antenna design are proposed. This three-port microstrip antenna composed of two substrates and three metal layers is fed by a microstrip line at bottom layer and double metal vias between top and bottom layers, whose diameters are different. Two high-impedance microstrip lines at top layer are connected to the microstrip antenna to feed the subarray at the two sides. By changing the size, spacing and offset of the double metal vias and the length of the opening stub at the end of bottom microstrip line, we can exactly control the power division ratio and phase difference of the two ports at top layer. The rules of designing this antenna are generalized and applied to the synthesis of array antenna of 77 GHz vehicle collision-warning radar system in this thesis. In order to minimize the size of the system, antenna and RF circuit have to be placed at different layers, therefore, signals need to transfer from bottom to top layer to feed antenna. Besides, in case the feeding structure do not need to placed at the center of antenna array, the degrees of freedom of designing RF circuit layout at bottom layer would increase. The three-port microstrip antenna we introduced has this two characteristics: layer-transfer function and ability to synthesize offset-feed antenna array.